DE102013111235A1 - Arrangement for the optical measurement of one or more physical, chemical and / or biological process variables of a medium - Google Patents

Abstract

The invention relates to an arrangement (1) for the optical measurement of one or more physical, chemical and / or biological process variables of a medium (2), wherein the arrangement (1) comprises a housing (3) and the housing (3) for receiving a measuring device (4) is designed to determine the physical and / or chemical process variables, wherein in the housing (3) at least one window (5) is arranged and at least the window (5) is in contact with the medium, and wherein a vibration transmitter (6) for transmitting Sound wave is provided, characterized in that the window (5) is rigidly connected to the housing (3), the vibration transmitter (6) in a peripheral module (7) with a module housing (8) is arranged, the peripheral module (7) is arranged so that the vibration generator (6) sends the sound waves in the direction of the window (5), wherein the sound waves pass through the module housing (8) at a passage surface (9), and the peripheral module (7) so on ordered is that medium (2) is in the range of window (5) and passage surface (9).

Description

The invention relates to an arrangement for the optical measurement of one or more physical, chemical and / or biological process variables of a medium. The arrangement comprises in particular a measuring device, in particular a sensor.

A major problem of sensors that measure in a particular medium, especially liquid, is their contamination. These contaminations are caused by deposits, biofilms, etc. In almost all types of sensors (electrochemical, biochemical, optical, ...), such impurities can lead to false readings or even complete failure of the sensor, with contamination of membranes, electrodes, active surfaces, optical windows, etc. being considered critical to be evaluated.

As an example, this should be explained using a turbidity sensor. Basically, however, the problem occurs with all sensors that measure in liquid and require a certain cleanliness of certain sensor components. In particular, similar process variables such as the solids content or the sludge level should also be mentioned here. Measuring instruments that are suitable for determining the appropriate process variables are offered and distributed by the Endress + Hauser Group in a large variety of variants.

Usually, the sensors are arranged in a sensor housing, and the determination of the process variable is often done optically. In this case, electromagnetic waves of a specific wavelength are transmitted by at least one transmitting unit, scattered by the medium to be measured and received by a receiving unit. Depending on the dispersion, it is possible to deduce the parameter to be measured.

The electromagnetic waves pass through the housing through a permeable to the electromagnetic waves material, often a corresponding window. In the course of time, soiling will occur on the window and the electromagnetic waves will not be able to pass (unhindered). There are distortions of the measurement to the failure of the sensor.

In order to maintain the functionality of the sensor, the window must be cleaned.

The following methods of cleaning are known: manually, by wiper, with air, by flushing or by means mounted in the housing vibration or ultrasonic transducer.

For manual cleaning, the sensor must be removed from the process. If it is an application in a pipeline, either the process must be stopped or an expensive retractable fitting used. In hygienic applications, wiper, air and flush cleaning are eliminated due to dead spaces.

The DE 43 17 068 C2 shows an attached directly to the window ultrasonic transmitter. As a result, not only the window, but also the housing is set in vibration. As a rule, the installation space for an ultrasonic transmitter in the sensor is very limited. As a result, low-power transmitters must be used. In addition, the energy transfer of the ultrasound into the liquid due to the window wall thickness is not optimal. In combination with the limited electrical power available in the sensor, this leads to a low cleaning effect.

The DE 90 15 235.2 discloses a turbidity sensor having windows wherein the windows are continuously vibrated by a vibrator. Even so, highly accurate measurements are not possible.

The US 5,889,209 shows a submersible ultrasonic transmitter for a sensor for dissolved oxygen in aqueous media, which are in relatively open containers such as in a river, in the sea or a basin. The ultrasonic transmitter and the sensor are both completely under water and the ultrasonic transmitter sends ultrasound waves with a duration of 5 s to 90 s in the direction of the diaphragm at a small spatial distance of 4 mm to 10 mm to the sensor and a time interval of 5 min to 120 min of the sensor. Due to the complete immersion and the water contact, hygienic applications do not seem feasible.

The DE 198 11 876 B4 discloses a vibrator mechanically coupled to the window with the window suspended elastically in the housing. For the generation of vibrations, a piezoelectric transducer is usually used. Its activation requires large voltages and currents. This results in the immediate vicinity of the measuring system electromagnetic fields, which can lead to EMC problems, especially with regard to the measuring electronics. As a rule, the installation space for an ultrasonic transmitter in the sensor is very limited. As a result, low-power transmitters must be used. In addition, the energy transfer of the ultrasound into the liquid is not optimal due to the window wall thickness. In combination with the limited electrical power available in the sensor, this leads to a low cleaning effect.

The invention is therefore based on the object to propose an effective cleaning of the window, which does not affect the measurement.

The object is achieved by an arrangement and wherein the arrangement comprises a housing and the housing is designed for receiving a measuring device for determining the physical and / or chemical process variables. At least one window is arranged in the housing and at least the window is in contact with the medium. In addition, a vibration generator is provided for transmitting sound waves. The window is rigidly connected to the housing, the vibration transmitter is arranged in a peripheral module with a module housing, and the peripheral module is arranged so that the vibration transmitter sends the sound waves in the direction of the window. Thus, the sound waves pass through the module housing at a passage area, and the peripheral module is arranged so that medium is in the region of the window and passage area. Thus, the window can be cleaned optimally. "Window" in the sense of this invention is to be understood as an optical window, that is, for example, in use in a turbidity sensor, but also as a non-optical window, for example in use in a pH sensor or a conductivity sensor.

In a preferred embodiment, the peripheral module is mechanically connected to the housing. "Mechanical" is to be seen as positive (by an appropriate arrangement), non-positive (by screwing), or as cohesive (by gluing) connection.

To improve the cleaning performance is preferably formed by the sound waves cavitation in the medium.

For retrofitting the peripheral module is designed as a plug-in module to the housing. So it can also be retrofitted sensors.

In one embodiment, the vibration generator is designed as a piezoelectric transducer. So it can be inexpensively and relatively easily the sound waves are generated.

The vibration transmitter sends a frequency of sound waves from 16 kHz to 200 kHz. This has turned out to be the optimal cleaning frequency.

In an advantageous embodiment, the vibration generator is configured as a radial oscillator, thickness vibrator or shear oscillator. There is thus a lot of freedom in terms of the design of the vibrator, and thus of the arrangement.

In a special embodiment to increase the amplitude - and thus the cleaning performance, the vibration generator is designed as a coupling oscillator.

For optimal coupling, the frequency of the sound wave corresponds to a resonant frequency of the vibration generator.

In a preferred embodiment, a control unit is provided, which controls the vibration transmitter and the measuring device.

The measuring device is preferably a turbidity sensor.

In an advantageous embodiment, the housing for receiving in a fitting, in particular in a plunger fitting, designed. The arrangement can thus be driven easily and quickly in the process.

The invention will be explained in more detail with reference to the following figures. Show it

1 the inventive arrangement in a first embodiment in the partial cross section, and

2 the inventive arrangement in a second embodiment in the partial cross section, and

3 the inventive arrangement in a third embodiment in partial cross-section.

In the figures, the same features are identified by the same reference numerals.

The arrangement according to the invention in its entirety has the reference numeral 1 ,

In the illustrated figures, the arrangement 1 for measuring medium 2 in a container 10 designed. The container can - as shown - be a pipe or pipe section. The use in a pipe is particularly advantageous because it can be transported away by the flow in the pipe the same dirt and debris. Still possible, however, is the use in an (open) basin, canal or other. The order 1 can also be used in a fitting, in particular an immersion fitting. The medium to be measured 2 is usually a liquid, often service and sewage. The arrangement is, for example, but also used in fresh water. Next is the arrangement 1 Application in non-aqueous media such as milk, yoghurt, ..., (fruit) juices or slurries.

Due to the geometry and the embodiments described below is the arrangement 1 basically also suitable for hygienic applications. The order 1 meets common hygiene requirements, such as the European Hygienic Engineering and Design Group (EHEDG) or the Food and Drug Administration (FDA) requires.

For measuring at least one physical, chemical and / or biological process variable, the arrangement comprises 1 a measuring device 4 , Without limitation, the measuring device 4 designed in the figures as turbidity sensor. The measuring device 4 is in a housing 3 positioned. By suitable means, for example a flange 11 , is the case 3 with the container 10 connected. About a connection 12 is the measuring device 4 connected to a control unit (not shown). The control unit is about a transmitter, control center etc.

The turbidity sensor 4 has at least one light source, often an LED, which is towards the medium 2 Sends light. In this case, "light" in the context of this invention should not be limited to the visible range of the electromagnetic spectrum, but be understood as electromagnetic radiation of any wavelength, especially in the far ultraviolet (UV) and infrared (IR) wavelength range.

The light passes through the housing 3 by an optical window transparent to the emitted light source 5 , The window 5 for example, a solid optical window made of a hard mineral material such as sapphire. window 5 and housing 6 are rigidly connected, in particular windows 5 and housing 3 medium-tight interconnected.

Of course, if the arrangement is used in a non-optical application, the window is designed as a non-optical window. If the arrangement is used, for example, in a pH sensor, the window is to be understood as a corresponding separating layer between the medium and the pH-sensitive sensor component. As another example, in conductivity sensors, the window is to be understood as the area of the housing in which the magnetic flux generated by the coils enters the medium to be measured.

The light is then scattered by the medium. There are several ways that the scattered light should now be detected. Examples are the detection at a 90 ° or 135 ° angle to the direction of irradiation. However, this should not be part of this invention and can be read in popular textbooks.

As materials for the arrangement 1 , as the case 3 and the peripheral module 7 Stainless steel, plastic or a ceramic can be used. As already mentioned, the turbidity sensor is often used in drinking water, wastewater or non-aqueous media. The materials are chosen so that they are suitable for use in sewage, for example. Plastic must therefore be a suitably resistant plastic such as PTFE or similar. be.

Naturally, the window is polluted by the use in wastewater over time 5 , According to the invention, a vibration generator 6 proposed for cleaning the window.

The vibrator 6 sends sound waves in the direction of the window 5 , The vibrator 6 is designed as a piezoelectric transducer and sends sound waves with a certain frequency, which is between 16 kHz to 200 kHz. The vibrator 6 So it sends in the ultrasound. Preferably, a frequency of 40 kHz is used. Preferably, the transducer transmits at a frequency corresponding to the resonant frequency of the piezoelectric transducer. For the vibration transmitter 6 Only limited power is available. The performance of the vibration transmitter 6 are about 50 W. The vibration generator 6 is turned on about every few minutes, for example every minute or every two minutes for about 500 ms. This frequent rhythm is chosen because it has been shown that immediately after switching on the vibrator 6 the best cleaning performance is achieved.

The vibrator 6 is in a peripheral module 7 arranged. 1 shows a first embodiment. Ideally, this is the peripheral module 7 just opposite the window 5 arranged. The vibrator 6 sends sound waves in the direction of the window 5 and cleans it thus. Thus, the sound waves at the proposed frequency of 16 kHz to 200 kHz can spread optimally and thus the cleaning effect is maximum, a distance from vibration sensor 6 to window 5 suggested from about 40 mm to 100 mm. The peripheral module 7 includes a module housing 8th ; the sound waves penetrate the module housing 8th at a passage area 9 , So that the sound waves are optimally coupled, a "coupling paste" is used.

The module housing 8th can also be designed as a kind of tub, such as stainless steel, either in the container 10 is integrated or through an opening in the container 10 into the medium 2 protrudes. A direct contact with the medium to be measured 2 is thus avoided and the arrangement 1 is basically suitable for hygienic applications. For a good transmission of the sound waves is the tub is equipped with a thin, constant wall thickness. Thus, the peripheral module becomes 7 even easier to retrofit.

The vibrator 6 will have a connection 13 driven. The control can be effected by the already mentioned control unit or by a second, other, unit. The configuration in 1 This only makes sense for pipes with a diameter that is significantly smaller than the transmission width of the vibration sensor 6 ,

2 shows a second embodiment of the invention. Here is the peripheral module 7 on the housing 3 ie module 7 and housing 3 are mechanically coupled. The peripheral module 7 can be configured as a plug-in module, ie such a cleaning device can be retrofitted. The module 7 but can also by common methods such as gluing, screws, rivets, etc. with the housing 3 get connected. It is important to ensure that no medium between module 7 and housing 3 can penetrate and out of the container 10 exit. Will the arrangement 1 used in a fitting, the peripheral module can 7 also be attached to the valve.

In 2 is the vibrator 6 designed as a radial oscillator and thus encloses the medium 2 facing the end of the measuring device 4 , So can the window 5 optimally hit by the sound waves and thus cleaned.

3 shows a third embodiment. Here is the vibration generator 6 designed as a thickness oscillator. The vibrator 6 is opposite the window 5 and can thus optimally hit and clean it with sound waves.

The mentioned embodiments with regard to switch-on interval or distance between vibration transmitter 6 and windows 5 apply analogously to the examples in 2 and 3 ,

The principle underlying cleaning is cavitation. The vibrator 6 Couples sound waves into the medium 2 , resulting in (medium) waves with positive and negative pressure. When a vacuum wave hits the dirty window 5 forms a cavity filled with steam. This steam condenses abruptly when hitting the next overpressure wave, causing pollution at the window 5 attach, be solved.

LIST OF REFERENCE NUMBERS

1

 arrangement

2

 medium

3

 casing

4

 measuring device

5

 window

6

 vibrator

7

 Peripheral module

8th

 module housing

9

 Passage area

10

 container

11

 flange

12

 connection

13

 connection

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4317068 C2 [0009]
• DE 9015235 [0010]
• US 5889209 [0011]
• DE 19811876 B4 [0012]

Claims (12)

Arrangement ( 1 ) for the optical measurement of one or more physical, chemical and / or biological process variables of a medium ( 2 ), the arrangement ( 1 ) a housing ( 3 ) and the housing ( 3 ) for receiving a measuring device ( 4 ) is designed to determine the physical and / or chemical process variables, wherein in the housing ( 3 ) at least one window ( 5 ) and at least the window ( 5 ) is in contact with the medium, and wherein a vibration transmitter ( 6 ) is provided for transmitting sound waves, characterized in that the window ( 5 ) rigidly with the housing ( 3 ), the vibration transmitter ( 6 ) in a peripheral module ( 7 ) with a module housing ( 8th ), the peripheral module ( 7 ) is arranged so that the vibration generator ( 6 ) the sound waves in the direction of the window ( 5 ), where the sound waves are the module housing ( 8th ) at a passage surface ( 9 ), and the peripheral module ( 7 ) is arranged so that medium ( 2 ) in the range of windows ( 5 ) and passage area ( 9 ) is located. Arrangement ( 1 ) according to claim 1, characterized in that the peripheral module ( 7 ) with the housing ( 3 ) is mechanically connected. Arrangement ( 1 ) according to claim 1 or 2, characterized in that by the sound waves cavitation in the medium ( 2 ) arises. Arrangement ( 1 ) according to at least one of claims 1 to 3, characterized in that the peripheral module ( 7 ) as a plug-in module to the housing ( 3 ) is configured. Arrangement ( 1 ) according to at least one of claims 1 to 4, characterized in that the vibration transmitter ( 6 ) is designed as a piezoelectric transducer. Arrangement ( 1 ) according to at least one of claims 1 to 5, characterized in that the vibration transmitter ( 6 ) transmits a frequency of the sound waves from 16 kHz to 200 kHz. Arrangement ( 1 ) according to at least one of claims 1 to 6, characterized in that the vibration generator ( 6 ) is designed as a radial oscillator, thickness oscillator or shear oscillator. Arrangement ( 1 ) according to claim 7, characterized in that the vibration generator ( 6 ) is designed as a coupling oscillator. Arrangement ( 1 ) according to at least one of claims 1 to 8, characterized in that the frequency of the sound wave of a resonant frequency of the vibration generator ( 6 ) corresponds. Arrangement ( 1 ) according to at least one of claims 1 to 9, characterized in that a control unit is provided which the vibration transmitter ( 6 ) and the measuring device ( 4 ). Arrangement ( 1 ) according to at least one of claims 1 to 10, characterized in that it is in the measuring device ( 4 ) is a turbidity sensor. Arrangement ( 1 ) according to at least one of claims 1 to 11, characterized in that the housing ( 3 ) for receiving in a fitting, in particular in a plunger fitting, is configured.

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